Display screen or portion thereof with a graphical user interface



FIG. 1 is a front view of a display screen or portion thereof with agraphical user interface showing our new design; and,

FIG. 2 is a front view thereof, provided to illustrate an exampleenvironment.

The long and short dashed broken line showing of a mobile terminal inFIG. 1 forms no part of the claimed design. The mobile terminal, displayscreen, and the text/words, numbers, symbols, and images of thegraphical user interface shown in broken lines in FIGS. 1 and 2 form nopart of the claimed design.

CLAIM The ornamental design for a display screen or portion thereof witha graphical user interface, as shown and described.